Elastomeric materials are known and have been used in numerous applications where resistance to permanent deformation is important. Elastomeric materials are generally prepared by mixing an elastomer with a curing agent and then curing the mixture in a mold at elevated temperatures for a period of time. The cured elastomer is then resistant to permanent deformation but yet can no longer be melt processed or reused without degradation.
Thermoplastic materials are also known and can be molded or otherwise shaped and reprocessed at temperatures above their melting or softening point. Thermoplastic materials, however, are not resistant to permanent deformation, particularly at elevated temperatures.
Thermoplastic elastomers are also known and exhibit both thermoplastic and elastomeric properties. These materials are capable of being reprocessed like thermoplastics but yet have desirable physical properties like elastomers. Shaped articles that are resistant to permanent deformation can be formed from thermoplastic elastomers by extrusion, injection molding or compression molding without the time-consuming cure step required with conventional elastomeric materials, thereby improving thruput and reducing energy cost. Additionally, since these materials are thermoplastic, scrap and the articles themselves can be reprocessed.
The preparation of thermoplastic elastomeric compositions based on thermoplastic polymers and vulcanized rubbers, according to the method known as "dynamic vulcanization" is known in the art and is described in particular in U.S. Pat. Nos. 3,037,954; 3,758,643; 3,806,558; 3,862,106; and 3,835,201. Other methods of preparing thermoplastic elastomers by cross-linking an elastomer, usually in the presence of a thermoplastic, are also described in the patents summarized below: U.S. Pat. Nos. 4,059,651; 4,311,628; and 4,707,519 disclose phenolic induced cross-linking of blends of ethylene-propylene-diene terpolymer (EPDM) in the presence of olefin resins; U.S. Pat. No. 3,957,919 discloses peroxide induced cross-linking of blends of polyethylene and EPDM in the presence of polypropylene; U.S. Pat. No. 4,232,132 discloses the peroxide induced cross-linking of ethylene vinyl acetate copolymer in the presence of polypropylene; U.S. Pat. No. 4,613,533 discloses the cross-linking of ethylene vinyl acetate polymers in the presence of vinyl chloride; and U.S. Pat. No. 4,758,629 discloses the cross-linking of ethylene-acrylate-glycidyl acrylate terpolymer in the presence of polyolefins using known cross-linking agents for epoxy resins.